基于SD的耕地与生态用地联合调配策略仿真与优选——以天津市为例

以复杂系统模拟为手段，以生态与经济双赢为目标，进行耕地与生态用地的联合调配策略的设计、仿真与优选，旨在通过两种土地的合理调配，在保障粮食安全前提下，以生态修复促超负荷耕地休养。在人口、经济、耕地和生态用地各子系统及其要素分析的基础上，以耕地污染严重、后备用地紧缺、地处《全国主体功能区规划》中的优化开发区域——天津市为例，建立耕地与生态用地联合调配的系统动力学模型（Tianjin System Dynamic，TSD）并进行有效性检验。结果显示，模型具有较好的稳定性，而且仿真值与实际值误差<5%，因此模型有效。在确定模型有效之后，应用TSD模型模拟不同策略下的天津市2016—2025年耕地与生态用地联合调配结果。本文设置了两种与系统惯性发展相比较的调配策略——耕地资源省域内调配策略和耕地资源跨省域调配策略，并对上述3种情景分别进行仿真。结果显示：1）按当前的惯性趋势发展，2025年受损耕地可以得到修复，耕地数量能够满足耕地红线要求，生态安全也能够得到保障，但是耕地产出压力会突破警戒阈值，因此存在潜在的粮食危机；2）耕地与生态用地省内调配情景下，虽然可以降低耕地的产出压力，但生态安全有所减损，而且耕地产出压力仍高于警戒阈值；3）允许耕地跨省域调配情景下，耕地产出压力可以降低到警戒值之下，而且生态安全能够得到更好的保障。比较3种仿真结果可知，允许耕地跨省域占补情景下的耕地与生态用地联合调配效果最好，可以使耕地与生态用地联合调配更灵活，更好地保障生态安全和粮食安全。以上说明本文所构建的TSD模型进行耕地与生态用地联合调配研究是有效的，一方面可以为耕地与生态用地联合调配策略的优选提供支撑，另一方面为后备耕地紧缺的优化开发地区确定跨省域占补数量提供科学依据。

Development of strategies for joint allocation of cultivated land and ecological land in Tianjin based on system dynamics

Tianjin was prioritized as a functional development region in China, but its cultivated land is seriously polluted and exhausted. This study adopted complex systems modeling to develop a land allocation strategy that allows food production to be secured and land recuperated in Tianjin, where is an optimum development area in the National Main Functional Areas Planning with seriously polluted cultivated land and scarcely reserved land resources. Upon analyzing the subsystems of population, economy, and cultivated land and ecological land, a restoration model, named Tianjin System Dynamics (TSD), was developed to optimize joint allocation of cultivated land and ecological land. Validity test showed that the model had a good stability and the prediction error was < 5%. The model was then used to simulate land allocation between cultivated land and ecological land from 2016 to 2025 for Tianjin under the following strategies:inertial, in-provincial allocation, and inter-provincial allocation of cultivated land resources. The analysis showed that, with the current practice, damaged cultivated land could still be repaired, but only by 2025. Cultivated land could then still be maintained above the red line minimum, and the land ecology could still be preserved. However, food production might not be secured, as the productivity of cultivated land would be pressed to drop to the threshold. The in-provincial allocation of cultivated land resources would alleviate the pressure on cultivated land while still maintaining production above the threshold, but the ecological security of the land would be impaired, the output pressure of cultivated land still be higher than the warning threshold. In contrast, the scenario of the inter-provincial allocation of cultivated land resources could minimize land pressure to below the warning value, and improve land ecological security as a result of its flexibility. The TSD model developed optimized allocation between cultivated land and ecological land for Tianjin, and could be used for land restoration planning for other regions that are lacking in land reserve.